Nucleic acid-based delivery system delivering platinum drugs cooperates with siRNA for potentiated chemo-immunotherapy by reducing phosphatidylserine exposure and activating the cGAS–STING pathway

Chemotherapeutic drugs, such as cisplatin and phenanthriplatin (PhenPt), as STING agonists to induce DNA damage and activate the cyclic GMP–AMP synthase-stimulator of interferon genes (cGAS–STING) signaling pathway provides a potential strategy for clinical chemo-immunotherapy. However, treatment with Pt-based drugs leads to irreversible ectopia of phosphatidylserine (PS), a major component of the intracellular membrane, to the surface of the cancer cells by enzymes (Xkr8). Exposed PS can bind to immune cell receptors and inhibit the presentation of tumor antigens, leading to immunosuppression and attenuation of chemotherapy. Herein, we report a novel approach to enhance chemo-immunotherapy by constructing siRNA targeted Xkr8 (siXkr8)-mediated tetrahedral framework nucleic acid nanogel structure concurrently loaded with PhenPt (siXkr8-FNG/PhenPt) for co-delivery of siRNA and Pt-based drugs. The results showed that siXkr8-FNG/PhenPt can not only be used as an efficient delivery carrier to deliver siXkr8, block the expression of Xkr8, reduce the exposure of PS on the cancer cells surface, but also act as an immune stimulant to activate cGAS–STING pathway, effectively improve the immunosuppressive microenvironment, produce antitumor immune response, and inhibit tumor growth and metastasis. Overall, this new delivery system is important for improving the effect of Pt-based drug chemotherapy, inducing immune enhancement and nucleic acid drug delivery.